1. Technical Field
The present application relates to a method for determining the length of a path traveled by a vehicle using an onboard unit carried by the vehicle, the unit generating a sequence of readings of the own position thereof.
2. Background Art
Onboard units (OBUs) are used in particular by road toll systems so as to be able to determine and subsequently impose tolls on paths traveled by a vehicle carrying the OBU. For this purpose, an OBU determines its own location, for example, in a global navigation satellite system (GNSS) or in a public land mobile network using several stationary transceivers and thus generates a sequence of position readings (“position fixes”). Each of the generated position readings is subject to measuring inaccuracies, requiring editing of the sequence that is generated.
For the purpose of editing, it is known to compare the generated position readings to a digital road map modeling the road system (map matching). To this end, the respective nearest road segments are determined as having been driven. Depending on the configuration, the OBU for this purpose either transmits the position readings to a back office of the road toll system, where the map matching is carried out (“thin-client OBU”), or the digital road map is stored directly in the OBU, where the map matching is also carried out (“thick-client OBU”).
However, map matching methods have the drawback that the accuracy of the path length determination is limited by the segment resolution of the digital road map. The lengths of the paths in fact traveled by a vehicle frequently deviate from the lengths of the digitally modeled road segments: for example in the region of curves, intersections or traffic circles, the path actually driven is dependent on the driving direction of the vehicle, while the segment lengths of the digital road map are generally modeled independently thereof.
On the other hand, it would also be problematic to determine the path lengths based on the position readings because frequent inaccuracies of the position readings conflict with reliable, robust path length determination.